1. Field of the Invention
The present invention relates to video discs and to a method for mass producing replicate video discs from a master video disc, and more particularly to a mass production process wherein the replicate discs are contact prints of the master disc.
2. Description Relative to the Prior Art
A master video disc is a high quality recording of video program material. From the master disc, it is desirable to mass produce replicate discs for consumer use. The replicate discs should therefore be priced for the consumer market; price being a function of the cost of materials to manufacture the replicate discs as well as the cost of the replicating process itself. One very attractive duplicating process is that of contact printing. Contact printing is inexpensive, straightforward and reliable when it works. Unfortunately, contact printing is not well suited to the replication of video discs for two major reasons: (1) Video information recorded on a video disc is in the form of an array of elongated circular apertures only a few wavelengths of light in size; diffraction by such apertures causes contact between the master disc and the replicate disc to be extremely critical. Even a slight separation occurring between the master disc and the replicate disc during exposure will result in a large drop in the fidelity of the recorded micro-imagery. (2) The typical video disc is about 30 cm (twelve inches) in diameter and has literally billions of micrometer sized apertures covering the disc, thereby making it necessary to maintain intimate master-to-replicate contact over the entire disc surface--a very difficult, if not impossible, requirement.
Over a 30 cm disc surface it is almost a certainty that intimate contact will be lost over substantial areas due to the presence of dust, dirt, etc. Loss of intimate contact between the master disc and the replicate disc is accompanied by a decrease in the quality of the replicate image which, at best, results in poor video information transfer and, in the more severe instances, results in complete loss of the video signal. It would, therefore, seem apparent that if contact printing is to be a viable method of mass producing replicate video discs from a master disc, the critical problem of achieving intimate contact and maintaining such contact over the entire disc surface would have to be solved. As a corollary to the intimate-contact problem, it will be appreciated that a protective coating on the master would severely degrade contact printed images.